Metallographic Observation of the Monoclinic‐Tetragonal Phase Transformation in ZrO ₂

Abstract

The monoclinic‐tetragonal phase transformation of ZrO 2 was examined with a vacuum hot‐stage microscope. Polished sections of vacuum‐sintered 99.7% pure ZrO 2 were observed from room temperature to 1300°C. The rapid formation of platelet substructure within ZrO 2 grains in the temperature range 1050° to 1150°C was associated with the heating transformation. Photomicrographs and motion pictures were taken of the specimen as the transformation progressed. The surface deformation was irreversible, preventing observation of the phase inversion on cooling. From these hot‐stage studies, supplementary DTA, X‐ray, and thermal expansion data, and other existing information, it is concluded that the transformation is of the diffusionless, athermal type, characteristic of Fe‐Ni martensitic transformations.